This invention relates to an infrared ray sensing device.
Wavelengths of visible rays reside in the range of approximately 350-700 nm. Rays having wavelengths below 350 nm are in an ultraviolet range. Rays having wavelengths above 700 nm are in an infrared range. The ultraviolet and infrared rays are invisible.
Infrared rays in a long wavelength range are radiated as heat. As the wavelength of the infrared ray increases, the related transmissivity rises. For example, infrared rays having large wavelengths can travel for long distances in a fog or smoke.
These characteristics of infrared rays are used in several known image pickup systems which can image an object under dark or foggy conditions. Infrared ray sensors are generally of the heat type and the photon type. In the heat-type sensors, variations in their temperatures which result from thermal energies of incoming infrared rays are detected through changes in a physical parameter or quantity such as resistance or charge quantity. The photon-type sensors directly detect photons of infrared rays. Some of the heat-type sensors use pyroelectric sensing elements dispensing with cooling, and typically include a film of polyvinylidene fluoride (PVF.sub.2), a thin plate of a single crystal of triglycinium sulphate (TGS), triglycinium fluoroberyllate (TGFB), deuterium triglycinium fluoride (DTGS), deuterium triglycinium fluoroberyllate (DTGFB), or a ceramic of lead titanate (PbTiO.sub.3). The photon-type sensors have semiconductor sensing elements including a substance such as silicon (Si), indium antimony (InSb), or mercury cadmium tellurium (HgCdTe).
Image detectors using infrared ray sensors are generally of three types, that is, a mechanical scanning type, a solid scanning type, and an electron beam scanning type. A thermography is a typical image detector of the mechanical scanning type. A monolithic camera device including infrared ray sensors on charge coupled devices (CCD) is a typical image detector of the solid scanning type. A pyroelectric camera tube is a typical image detector of the electron beam scanning type. All of these image detectors operate in a passive manner such that an object is imaged on the detectors through infrared rays emitted from the object and then the image is converted into an electric signal. The passive-type image detectors cannot sense an object when the object does not emit any infrared rays.
In addition, there are active-type detecting systems which operate in a manner such that infrared rays are positively applied to an object and the object is detected through the infrared rays reflected by the object.
Recently, there is an increasing need to image an object under dark conditions and to grasp the situation in various calamities and disasters. It has been proposed and studied that an infrared ray sensing device is used in detecting a firing point, grasping the situation of damages to objects and facilities in flames, and grasping the situation of peripheries for saving lives. Conventional infrared ray sensing devices are unsatisfactory from the standpoint of heatproof characteristics. Specifically, the conventional infrared ray sensing devices can not operate normally when they are close to flames having temperatures of one thousand and several hundred degrees of Celsius.
Generally, the wavelength distribution of energies radiated from surfaces of a black body, the wavelength of the maximal radiation quantity, and the total radiated energies depend on the temperature of the black body in accordance with well-known Planck's law of radiation, Wien's displacement law, and Stefan-Boltzmann's law, respectively.
FIG. 6 shows the wavelength distribution of energies radiated from a black body at various temperatures. It is understood from FIG. 6 that the place of a fire radiates infrared rays in a wide range of wavelengths and that temperatures of peripheries of the fire place are much increased by radiated heats. Conventional infrared ray sensing devices can operate normally at temperatures below approximately 70.degree. C. Accordingly, the conventional sensing devices cannot be used in or near the place of a fire if they have no heat protection.